Worked on enhancing the reliability of the Query Planner in the apache/calcite repository by addressing a complex bug related to correlated subquery correlation tracking. Focused on correcting the indexing of correlated variables within subqueries after filter join rules were applied, which improved the accuracy of predicate classification and ensured greater integrity of execution plans for complex queries. Utilized Java and SQL to implement the fix, drawing on expertise in database optimization and query planning. Demonstrated strong debugging and code review skills, contributing to more predictable query performance and reducing the risk of incorrect execution plans in critical database workflows.